Certain childhood neuropsychiatric disorders, including Sydenham's chorea, Obsessive Compulsive Disorder (OCD) and Tourette's disorder, appear to be mediated (for a subgroup of these patients) through antibodies produced against Group A beta-hemolytic streptococcal infections which cross-react with neurons within the basal ganglia and other regions. This has led to the identification of a clear subtype of patients with OCD and Tourette's disorder, who appear to ditinguishable from other forms of OCD and movement disorders. This subtype is identified by the acronym: PANDAS (Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections). Volumetric MRI examinations confirm basal ganglia involve in Sydenham's Chorea, while the preliminary success of immunomodulatory treatments, such as plasma exchange and intravenous immunoglobulin, suggests that the antibodies play an etiologic role. Ongoing treatment studies for this group of patients include immunomodulatory interventions (i.e. plasmaaphersis, intravenous immunoglobulins) for both Sydenham's Chorea and PANDAS. Additionally, a double-blind controlled trail of penicillin versus placebo is underway in a group of children with OCD or tic disorder related to PANDAS to determine if they have fewer and less severe exacerbations during the penicillin treatment.